Diborano: diferenças entre revisões

{{Info/Química

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==Estrutura e ligação==

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Diborane adopts a D_2h structure containing four terminal and two bridging hydrogen atoms. The model determined by [[molecular orbital theory]] indicates that the bonds between boron and the terminal hydrogen atoms are conventional 2-center, 2-electron [[covalent bond]]s. The bonding between the boron atoms and the bridging hydrogen atoms is, however, different from that in molecules such as hydrocarbons. Having used two electrons in bonding to the terminal hydrogen atoms, each boron has one [[valence electron]] remaining for additional bonding. The bridging hydrogen atoms provide one electron each. Thus the B₂H₂ ring is held together with four electrons, an example of [[3-center-2-electron bond]]ing. This type of bond is sometimes called a 'banana bond'. The lengths of the B-H_bridge bonds and the B-H_terminal bonds are 1.33 and 1.19 Å respectively, and this difference in the lengths of these bonds reflects the difference in their strengths, the B-H_bridge bonds being relatively weaker. The structure is [[isoelectronic]] with C₂H₆²⁺, which would arise from the diprotonation of the planar molecule [[ethene]].<ref>{{ cite journal | journal = [[Journal of Physical Chemistry A|J. Phys. Chem. A]] | year = 2005 | volume = 109 | issue = 5 | pages = 798–801 | author = G. Rasul, G. K. S. Prakash, [[George Andrew Olah|G. A. Olah]] | doi = 10.1021/jp0404652 | title = Comparative ab Initio Study of the Structures and Stabilities of the Ethane Dication C₂H₆²⁺ and Its Silicon Analogues Si₂H₆²⁺ and CSiH₆²⁺ | pmid = 16838949 }}</ref> Diborane is one of many compounds with such unusual bonding.<ref>{{cite journal | author= Laslo P | title= A Diborane Story | journal= Angewandte Chemie International Edition | year= 2000 | volume= 39 | pages= 2071–2072| doi= 10.1002/1521-3773(20000616)39:12<2071::AID-ANIE2071>3.0.CO;2-C | pmid=10941018 | issue= 12}} [http://www3.interscience.wiley.com/cgi-bin/abstract/72507084/ABSTRACT abstract]</ref>

The toxic effects of diborane are primarily due to its irritant properties. Short-term exposure to diborane can cause a sensation of tightness of the chest, shortness of breath, cough, and wheezing. These signs and symptoms can occur immediately or be delayed for up to 24 hours. Skin and eye irritation can also occur. Studies in animals have shown that diborane causes the same type of effects observed in humans. {{Citation needed|date=September 2009}}

 

 

 

* [http://www.inchem.org/documents/icsc/icsc/eics0432.htm International Chemical Safety Card 0432]

* [http://box27.bluehost.com/~edsanvil/wiki/index.php?title=Diborane Computational Chemistry Wiki]

* [http://www.epa.gov/oppt/aegl/results65.htm U.S. EPA Acute Exposure Guideline Levels]

 

 

[[ca:Diborà]]